Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

Annotations already declare readOnly=true, destructive=false, openWorld=true, and idempotent=false. The description adds important context beyond that: the payment model, $0.01/call, first 25 free, failed calls free, and that repeated calls are charged. It still does not mention rate limits or latency, so it is strong but not exhaustive.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Is the description appropriately sized, front-loaded, and free of redundancy?

The purpose, usage guidance, and alternative are front-loaded before pricing details. Some wording is redundant with the schema default and annotations, but the description remains readable and mostly efficient.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

With no output schema, the description carries the return-value burden and does so well: base fee per block, block fullness, priority-fee percentiles, and low/average/high aggregates. One optional parameter plus clear usage and pricing context makes it complete for an agent to call correctly.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

The single blocks parameter has 100% schema coverage with type, range, and default. The description repeats the range/default and gives an example, but does not add new meaning beyond what the schema already provides.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Does the description clearly state what the tool does and how it differs from similar tools?

Names the underlying eth_feeHistory call, the exact window (last N blocks), and the returned data (base fee, block fullness, priority-fee percentiles, window aggregates). It also distinguishes itself from eth_gas, which covers the current price alone.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Does the description explain when to use this tool, when not to, or what alternatives exist?

Gives explicit use cases: judge whether fees are rising, pick a priority fee, or time a transaction. It names the alternative eth_gas for current-price-only queries, so the selection boundary is clear.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.